Regulation by interleukin 2 of interleukin 2 receptors and gamma-interferon synthesis by human thymocytes: augmentation of interleukin 2 receptors by interleukin 2

The role of interleukin 2 (IL 2) on the expression of IL 2 receptors and on the synthesis of gamma-interferon (gamma-IFN) by human thymocytes was investigated. Human thymocytes isolated from specimens obtained during cardiac surgery of infants and children were induced with one or all of the following agents: IL 2, concanavalin A (Con A), and 12-O-tetradecanoylphorbol 13-acetate (TPA). The expression of IL 2 receptors and gamma-IFN titers were determined. The results indicate that thymocytes cultured in complete medium do not express receptors for IL 2, nor did IL 2 by itself induce the expression of IL 2 receptors. Con A induced the expression of IL 2 receptors by a moderate number of the thymocyte population and induced the synthesis of low amounts of gamma-IFN. Preincubation of thymocytes with TPA increased the response to Con A; both the number of thymocytes expressing receptors and the synthesis of gamma-IFN were increased. Addition of IL 2 to these cultures further augmented the expression of IL 2 receptors and gamma-IFN synthesis and resulted in the optimal expression of IL 2 receptors and maximal gamma-IFN synthesis. The expression of IL 2 receptors could be detected within 24 hr and preceded the induction of proliferation; it was therefore probably not due to the clonal expansion of a population of receptor-bearing thymocytes. Conversely, inhibition of IL 2 synthesis with dexamethasone (Dex) by thymocytes activated with Con A, or inhibition of the function of IL 2 receptors by anti-Tac, resulted in a decrease in the number of IL 2 receptor-bearing thymocytes activated with Con A, or inhibition of the function of IL 2 receptors by anti-Tac, resulted in a decrease in the number of IL 2 receptor-bearing thymocytes and of gamma-IFN synthesis. Thymocytes activated with TPA and Con A were more resistant to the inhibitory effects of Dex on the expression of IL 2 receptors than thymocytes activated with Con A alone. Maximal inhibition of the expression of IL 2 receptors and of gamma-IFN synthesis was achieved as a result of the synergistic effect of anti-Tac with Dex. Therefore, when IL 2 was prevented from binding to the receptors, and IL 2 synthesis was inhibited, the number of thymocytes expressing IL 2 receptors was sharply reduced and gamma-IFN synthesis was markedly inhibited.(ABSTRACT TRUNCATED AT 400 WORDS)     

Downregulation of ClC-2 by JAK2

JAK2 (Janus kinase-2) is activated by cell shrinkage and may thus participate in cell volume regulation. Cell volume regulatory ion channels include the small conductance Cl(-) channels ClC-2. The present study thus explored whether JAK2 influences ClC-2 activity. To this end, ClC-2 was expressed in Xenopus oocytes with or without wild type JAK2, active (V617F)JAK2 or inactive (K882E)JAK2 and the Cl(-) channel activity determined by dual electrode voltage clamp. Expression of ClC-2 was followed by a marked increase of cell membrane conductance. The conductance was significantly decreased following coexpression of JAK2 or (V617F)JAK2, but not by coexpression of (K882E)JAK2. Exposure of the oocytes expressing ClC-2 together with (V617F)JAK2 to the JAK2 inhibitor AG490 (40 μM) resulted in a gradual increase of the conductance. According to chemiluminescence JAK2 decreased the channel protein abundance in the cell membrane. The decline of conductance in ClC-2 and (V617F)JAK2 coexpressing oocytes following inhibition of channel protein insertion by brefeldin A (5 μM) was similar in oocytes expressing ClC-2 with (V617F)JAK2 and oocytes expressing ClC-2 alone, indicating that (V617F)JAK2 might slow channel protein insertion into rather than accelerating channel protein retrieval from the cell membrane. In conclusion, JAK2 down-regulates ClC-2 activity and thus counteracts Cl(-) exit, an effect which may impact on cell volume regulation.     

Oxygen-dependent H2O2 production by Rubisco

Oxygen and ribulose-1,5-bisphosphate dependent, H(2)O(2) production was observed with several wild type Rubisco enzymes using a sensitive assay. H(2)O(2) and d-glycero-2,3-pentodiulose-1,5-bisphosphate, a known and potent inhibitor of Rubisco activity, are predicted products arising from elimination of H(2)O(2) from a peroxyketone intermediate, specific to oxygenase activity. Parallel assays using varying CO(2) and O(2) concentrations revealed that the partitioning to H(2)O(2) during O(2) consumption by spinach Rubisco was constant at 1/260-1/270. High temperature (38 degrees C), which reduces Rubisco specificity for CO(2) versus O(2), increased the rates of H(2)O(2) production and O(2) consumption, resulting in a small increase in partitioning to H(2)O(2) (1/210). Two Rubiscos with lower specificity than spinach exhibited greater partitioning to H(2)O(2) during catalysis: Chlamydomonas reinhardtii (1/200); and Rhodospirillum rubrum (1/150).     

Polycystin-2 (TRPP2) Regulation by Ca2+ Is Effected and Diversified by Actin-Binding Proteins

Calcium regulation of Ca²⁺-permeable ion channels is an important mechanism in the control of cell function. Polycystin-2 (PC2, TRPP2), a member of the transient receptor potential superfamily, is a nonselective cation channel with Ca²⁺ permeability. The molecular mechanisms associated with PC2 regulation by Ca²⁺ remain ill-defined. We recently demonstrated that PC2 from human syncytiotrophoblast (PC2_hst) but not the in vitro translated protein (PC2_iv), functionally responds to changes in intracellular (cis) Ca²⁺. In this study we determined the regulatory effect(s) of Ca²⁺-sensitive and -insensitive actin-binding proteins (ABPs) on PC2_iv channel function in a lipid bilayer system. The actin-bundling protein α-actinin increased PC2_iv channel function in the presence of cis Ca²⁺, although instead was inhibitory in its absence. Conversely, filamin that shares actin-binding domains with α-actinin had a strong inhibitory effect on PC2_iv channel function in the presence, but no effect in the absence of cis Ca²⁺. Gelsolin stimulated PC2_iv channel function in the presence, but not the absence of cis Ca²⁺. In contrast, profilin that shares actin-binding domains with gelsolin, significantly increased PC2_iv channel function both in the presence and absence of Ca²⁺. The distinct effect(s) of the ABPs on PC2_iv channel function demonstrate that Ca²⁺ regulation of PC2 is actually mediated by direct interaction(s) with structural elements of the actin cytoskeleton. These data indicate that specific ABP-PC2 complexes would confer distinct Ca²⁺-sensitive properties to the channel providing functional diversity to the cytoskeletal control of transient receptor potential channel regulation.     

微胶囊固定化过氧化氢酶的制取及对H_2O_2的分解作用

以乙基纤维素为膜材,用溶液干燥法制取了微胶囊固定化过氧化氢酶,探讨了制取过程中明胶的加入对微胶囊产率及固定化过氧化氢酶活性的影响,同时论述了存放时间、温度以及环境ｐＨ值对微胶囊固定化过氧化氢酶稳定性的影响．深入研究了微胶囊固定化过氧化氢酶对Ｈ２Ｏ２的分解作用,获得了十分有意义的结果     

Degradation of 2-chlorobenzoate by Pseudomonas cepacia 2CBS

A bacterium was isolated from water by enrichment on 2-chlorobenzoate as sole source of carbon and energy. Based on morphological and physiological properties, this microorganism was assigned to the species Pseudomonas cepacia. The organism was designated Pseudomonas cepacia 2CBS. During growth on 2-chlorobenzoate, the chlorine substituent was released quantitatively, and a small amount of 2,3-dihydroxybenzoate accumulated in the culture medium. Mutants of Pseudomonas cepacia 2CBS were induced by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. Some of these mutants produced catechol from 2-chlorobenzoate. Other mutants accumulated the meta-cleavage product of catechol, 2-hydroxy-cis,cis-muconic acid semialdehyde. In crude cell-free extracts of Pseudomonas cepacia 2CBS, an enzyme was detected which catalysed the conversion of 2-chlorobenzoate to catechol. Molecular oxygen, NADH and exogenous Fe2+ were required for activity. Stoichiometric amounts of chloride were released. Experiments with 18O2 revealed that both oxygen atoms in the hydroxyl groups of the product were derived from molecular oxygen. Thus, the enzyme catalysing the conversion of 2-chlorobenzoate was identified as 2-chlorobenzoate 1,2-dioxygenase (1,2-hydroxylating, dehalogenating, decarboxylating). 2-Chlorobenzoate 1,2-dioxygenase from Pseudomonas cepacia 2CBS was shown to be a multicomponent enzyme system. The activities of catechol 2,3-dioxygenase and catechol 1,2-dioxygenase were detected in crude cell-free extracts. The activity of catechol 2,3-dioxygenase was 60 times higher than the activity of catechol 1,2-dioxygenase, indicating that catechol is mainly degraded via meta-cleavage in Pseudomonas cepacia 2CBS. No enzyme was found which converted 2,3-dihydroxybenzoate, suggesting that this compound is a dead-end metabolite of 2-chlorobenzoate catabolism. A pathway for the degradation of 2-chlorobenzoate by Pseudomonas cepacia 2CBS is proposed.     

Fe^2＋-H2O2体系降解壳聚糖

Fe2 -H2O2体系能够有效地降解壳聚糖,反应介质的pH值、反应时间、反应温度、Fe2 浓度及H2O2浓度等实验因素对壳聚糖的降解效果都有程度不同的影响,其中以反应介质的pH值和H2O2浓度对降解反应的影响为最大.在pH值为3～5时Fe2 -H2O2体系降解壳聚糖的活性最高.适当增大H2O2的用量可以增大壳聚糖的降解程度,但当其用量增大至一定程度后,壳聚糖降解产物分子量的下降趋势明显变缓.合理的Fe2 -H2O2体系降解壳聚糖的实验条件为:介质pH值3～5;温度,室温;时间60～90 min;壳聚糖:H2O2:Fe2 =240:12～24:1～2(摩尔比).     

Photooxidation of oligodeoxynucleotides by UO2(2+).

Photooxidation and consequent cleavage of oligodeoxynucleotides by the uranyl ion is greatly enhanced in the presence of a terminal 5'- or 3'-phosphate group. This enhanced cleavage is confined to nearby phosphodiester bonds in the case of a 5'-phosphate, but is less localized in the case of a 3'-phosphate. Several attempts to use a complementary oligodeoxynucleotide to direct a uranyl "warhead" against an oligodeoxynucleotide target were unsuccessful. Our results are most easily explained if we suppose that uranyl ions form coordination complexes with terminal phosphates and that, on photoexcitation, coordinated uranyl ions extract a hydrogen atom from the CH bond of a nearby deoxyribose residue.     

Translational control by RGS2

The regulator of G protein signaling (RGS) proteins are a family of guanosine triphosphatase (GTPase)–accelerating proteins. We have discovered a novel function for RGS2 in the control of protein synthesis. RGS2 was found to bind to eIF2Bϵ (eukaryotic initiation factor 2B ϵ subunit) and inhibit the translation of messenger RNA (mRNA) into new protein. This effect was not observed for other RGS proteins tested. This novel function of RGS2 is distinct from its ability to regulate G protein–mediated signals and maps to a stretch of 37 amino acid residues within its conserved RGS domain. Moreover, RGS2 was capable of interfering with the eIF2–eIF2B GTPase cycle, which is a requisite step for the initiation of mRNA translation. Collectively, this study has identified a novel role for RGS2 in the control of protein synthesis that is independent of its established RGS domain function.     

Effects of phosphorylation by CAK on cyclin binding by CDC2 and CDK2.

The cyclin-dependent protein kinases (CDKs) are activated by association with cyclins and by phosphorylation at a conserved threonine residue by the CDK-activating kinase (CAK). We have studied the binding of various human CDK and cyclin subunits in vitro, using purified proteins derived from baculovirus-infected insect cells. We find that most CDK-cyclin complexes known to exist in human cells (CDC2-cyclin B, CDK2-cyclin A, and CDK2-cyclin E) form with high affinity in the absence of phosphorylation or other cellular components. One complex (CDC2-cyclin A) forms with high affinity only after CAK-mediated phosphorylation of CDC2 at the activating threonine residue. CDC2 does not bind with high affinity to cyclin E in vitro, even after phosphorylation of the CDC2 subunit. Thus, phosphorylation is of varying importance in the formation of high-affinity CDK-cyclin complexes.     

G-quadruplex induced stabilization by 2'-deoxy-2'-fluoro-D-arabinonucleic acids (2'F-ANA)

The impact of 2'-deoxy-2'-fluoroarabinonucleotide residues (2'F-araN) on different G-quadruplexes derived from a thrombin-binding DNA aptamer d(G2T2G2TGTG2T2G2), an anti-HIV phosphorothioate aptamer PS-d(T2G4T2) and a DNA telomeric sequence d(G4T4G4) via UV thermal melting (T(m)) and circular dichroism (CD) experiments has been investigated. Generally, replacement of deoxyguanosines that adopt the anti conformation (anti-guanines) with 2'F-araG can stabilize G-quartets and maintain the quadruplex conformation, while replacement of syn-guanines with 2'F-araG is not favored and results in a dramatic switch to an alternative quadruplex conformation. It was found that incorporation of 2'F-araG or T residues into a thrombin-binding DNA G-quadruplex stabilizes the complex (DeltaT(m) up to approximately +3 degrees C/2'F-araN modification); 2'F-araN units also increased the half-life in 10% fetal bovine serum (FBS) up to 48-fold. Two modified thrombin-binding aptamers (PG13 and PG14) show an approximately 4-fold increase in binding affinity to thrombin, as assessed via a nitrocellulose filter binding assay, both with increased thermal stability (approximately 1 degrees C/2'F-ANA modification increase in T(m)) and nuclease resistance (4-7-fold) as well. Therefore, the 2'-deoxy-2'-fluoro-d-arabinonucleic acid (2'F-ANA) modification is well suited to tune (and improve) the physicochemical and biological properties of naturally occurring DNA G-quartets.     

Exostosin-like 2 regulates FGF2 signaling by controlling the endocytosis of FGF2

Background

Heparan sulfate proteoglycans are ubiquitously expressed on cell surfaces and in extracellular matrices, and are engaged in heparin-binding growth factor-related signal transduction. Thus, changes in the amounts, structures, and chain lengths of heparan sulfate have profound effects on aspects of cell growth controlled by heparin-binding growth factors such as FGF2. Exostosin glycosyltransferases (EXT1, EXT2, EXTL1, EXTL2, and EXTL3) control heparan sulfate biosynthesis, and the expression levels of their genes regulate the amounts, chain lengths, and sulfation patterns of heparan sulfate. Unlike EXT1, EXT2, and EXTL3, EXTL2 functions chain termination of heparan sulfate. Here, we examined the importance of EXTL2 in FGF2-dependent signaling.

2H magnetic relaxation of 2H2O absorbed by wool.

D2O absorbed by intact wool fibers was studied by solid-state 2H nuclear magnetic resonance (NMR) spectroscopy. In wool fibers swollen in D2O, the deuteron transverse magnetization and the spin-locked magnetization revealed a non-exponential decay. At least two NMR phases with different sets of the NMR relaxation parameters, T(1rho) (2H) and T2 2H, have been detected that may be a manifestation of two different morphological phases of the cortex of the fiber.